configure: enable mipsfpu for loongson platform.

mipsfpu supported by loongson 3a2000,3a3000,3a4000,2k1000, Fate tests passed.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

configure

@@ -4848,7 +4848,6 @@ elif enabled mips; then
                 enable fast_cmov
                 enable fast_unaligned
                 disable aligned_stack
-                disable mipsfpu
                 disable mipsdsp
                 disable mipsdspr2
                 # When gcc version less than 5.3.0, add -fno-expensive-optimizations flag.